Louis e



(NoModeL) L. E'. 8v M. LEVY.

SCREEN PUR VPHOTOIs/IEUNANlCAL PRINTING.

No. 492,333. Patented Feb. 21, 1893.,

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Y LOUIS E. LEVY AND MAX LEVY, OF PHILADELPHIA, PENNSYLVANIA; SAID LOUISE. LEVY ASSIGNOR TO MAX LEVY.

SCREEN FOR PHOTONIECHANICAL PRINTING.

SPECIFICATION forming part of Letters Patent No. 492,333, dated February21, 1893.`

Application filed April 13, 1891.

To all wh om t may concern.'

Be it known that we, LOUIS E. LEVY and MAX LEVY, both citizens of theUnited States, residing at Philadelphia, in the county of Philadelphiaand State of Pennsylvania, have jointly invented certain new and usefulImprovements in Grati'ngs or Screens which are Used in Making theso-called Half-Tone or Cross-Line Engravings, the following being afull, clear, and exact description, such as will enable others skilledin theI art to which it appertains to make and use the same,referencebeing had to the accompanying drawings, and to the letters markedthereon, which form a part of this specification.

This invention relates to improvements in gratings or screens which areintended for use in producing the so-called half-tone or crosslineengravings, the object being to provide a grating or screen in which thelines will be clear, sharp, solid and positive, so as be clearly definedand elfective in use.

In the accompanying drawings which illustratetheinvention the viewsrepresent a small part of the article enlarged or magnified.

Figure l is a plan view showing a glass plate with lines ruled in onedirection through the etching ground which has been applied thereto.Fig. 2 is a similar View vshowing the lines ruled so as to cross eachother. Fig. 3 is a vertical sectional view showing the appearance of theground after being ruled, and the glass before it is etched. Fig. 4 is avertical sectional view showing the plate after being etched, the groundbeing removed, the furrows being filled with opaque substance and theplate wiped or cleansed. Fig. 5 is a sectional view showingacompletedplate with a cover glass. Fig. 6 is a sectional view showing two similarplates connected to each other. Fig. 7 is a plan view of a portion of acompleted plate. Fig. 8 is a greatly enlarged sectional view.

In carrying out our invention a ground and polished plate of glass iscarefully selected, which is free from scratches or bubbles. This plateof glass is cleaned, and is covered with an etching ground, B,which maybe of any suitable composition that Will resist hydro-fiuoric Serial No.388,787. (No model.)

acid; which ground may be either iowed in solution, rolled, or dabbed onthe plate.

In practice the plate of glass A is covered with a coating of iodized orbromized collodion, and prepared in a solution of nitrate of silverexposed to light and the silver precipitated with a suitable deoxidizer.This affords a better basis for an etching ground than does the glassitself, for by absorbing the resisting ground causes it to hold morefirmly to the surface of the glass during the process off etching. Thelines A A are ruled through the etching ground so as to expose the glasswhere the composition or coating is removed by the etching implement.The ruling, which consists of straight lines in extremely closeproximity to each oth er-numberin g from one hundred and twenty to abouttwo hundred to the inch-are made by a dividing engine with a diamondpoint. These lines,which are usually parallel, may also cross each otherat right angles. The plate with the lines A ruled through the etchingground is then exposed to the action of the hydro-{iuoric acid, eitherliquid or fumes, the bac-l; of the plate being suitably protectedagainst the action of the acid. By means of the hydro-fluoric acid thefurrows, linear depressions or lines D are eaten into the glass to thedesired depth, while the other part "of the surface which is protectedby the etching ground is not affected by the acid and remains in itsoriginal condition. The plate is now washed, or otherwise cleansed, andthe whole of the lined surface is covered with a suitable opaquesubstance C, the body of which may be shellac and lamp black. Thisopaque substance Ois thoroughly rubbed into the furrows, lineardepressions or lines D, which are etched into the glass, and is allowedto partially dry and harden. The opaque substance is then removed fromthe surface of the glass so as to leave the lines furrows or lineardepressions filled with a hardened opaque paste, which is designated inthe drawings by the letter C. What we term the lines being the baseportion of the linear depressions or furrows D, which has been filledwith an opaque substance, as the upper inside edges of the 1ineardepressions or furrows, next to the surface, are slightly roughened bythe etching, which portion of the depressions or furrows is filled withthe cement D', which has the same index of refraction as the glass.

In etching the lines, linear depressions or furrows uponl the plate orglass, no matter how tine the etching tool may be or how much care maybe given to the manipulations, the action of the hydro-fiuoric acid, orother biting acid which eats into the glass, will mar, bite or abradethe upper surface or edges, either by biting into the glass at thispoint or finding its way beneath the etching ground, so that the furrowsor linear depressions instead of having sharp angular edges will berounded or abraded,which seriously affects the results sought to beattained by the grating or screen; therefore, to overcome theseimperfections the glass, after the opaque material has been placed inthe lines is wiped, so that said opaque material lies below theserounded edges. The glass and opaque material are then covered with asuitable material D', preferably balsarn of fir or Canada balsam, whichhas the same index of refraction that the glass has. By employing Canadabalsam the imperfections at the upper portions of the lineslineardepressions or furrows are filled with a substance'having the same indexof refraction as the glass, and the liability of aberration of the raysand unequal refrangibility are to such a degree removed that they neednot be considered in the use of such a grating or screen as is producedby our invention. A plate thus described may be protected on its ruledside by a cover glass, E, which may also be ruled in an oppositedirection from the plate to which it isattached, both plates beingprepared in the same manner, and Canada balsam is preferably used as amedium for joining together or connecting the two ruled glasses so as topractically produce a single plate in the center of which is thegratingor lines.

A plate constructed as hereinbefore described will not obstruct ordeflect the rays of light. The grating is not used to receive thepicture, nor is the picture or any part thereof at any time fixed on thegrating, but said grating in use is placed inside the camera between thelens and the sensitized plate upon which the photographic image is to beimpressed.

Having thus described our invention, what We claim as new, and desire tolsecure by Letters Patent, is-

1. A grating or screen for the purpose set forth, consisting of a glassplate having parallel linear depressions or furrows etched therein, thebase or lower portion of said linear depressions or furrows being filledwith an opaque paste to form lines, the portion of the lineardepressions or furrows above the lines being filled with a medium havingthe same index of refraction as the glass, for the purpose set forth.

2. A grating or screen for the purpose set forth, consisting of twoplates of glass each having parallel furrows, linear depressions orlines etched into one of its surfaces, the base portion of said furrows,linear depressions or lines being filled with opaque material, the linedglasses being cemented to each other, so that the lines will cross, by asubstance having substantially the sameindex of refraction as the glass.

3. As an improved article of manufacture a grating or screen forphotographic purposes in the production of half-tone plates, consistingof a plate of glass having parallel furrows, linear depressions or linesetched in one of the surfaces thereof, said furrows, linear depressionsor lines being partially filled with an opaque material to form lines,the upper portion of said furrows, linear depressions or lines above thelines being filled with a covering of Canadian balsam, for the purposeset forth.

4. Agrating or screen for photographic purposes in the production ofhalf-tone plates, consisting of two plates of glass one having finefurrows linear depressions or lines in its surface, said furrows lineardepressions or lines containing an opaque substance, the glass platesbeing cemented to each other to form one refracting medium with a rulingor network in its center, substantially as shown.

5. A grating or screen for photographic purposes in the production ofhalf-tone plates, consisting of two plates of polished glass each havingfurrows linear depressions or lines etched into their faces, saidfurrows linear depressions vor lines being partially filled with anopaque substance, the remaining portion of the furrows, lineardepressions or lines being filled with Canada balsam, said plates beingconnected to each other so that the lined portions are adjacent to eachother, for the purpose set forth.

LOUIS E. LEVY. MAX LEVY.

Witnesses:

J. C. FIREMAN, C. H. WALKER.

